Prague 4 and 6 - key differences?

I am moving to Prague from Canada in October. My family will follow in December. My question has to do with where to move. I have two girls, 8 and 3. They will both need to go to school. I noticed that the private schools tend to be in either prague 6 or prague 4. What are the main differences between prague 4 and 6 that I should know about?

For example, which area is friendlier to kids? Which has better accessibility to transportation? Which has a greater amount of english-speakers / Expats?